A Minneapolis homicide investigator testified on Friday that Derek Chauvin used "totally unnecessary" deadly force when kneeling on George Floyd's neck during an arrest last May that sparked global protests against police brutality.
Mr Chauvin, who is white, was fired by the city's police department the day after he was captured on video on top of a handcuffed Mr Floyd as the 46-year-old black man was dying. The 45-year-old former officer has pleaded not guilty to murder and manslaughter charges.
"Totally unnecessary," Lieutenant Richard Zimmerman told the jury when prosecutors asked what he thought of Mr Chauvin pressing his knee on Mr Floyd's neck for about nine minutes. "If your knee is on a person's neck, that can kill them."
Prosecutors from the Minnesota attorney general's office called Mr Zimmerman to testify in part to undermine a central argument in the defence case - that Mr Chauvin was correctly following his police training.
Mr Zimmerman, who joined the Minneapolis Police Department in 1985 and is now its most senior officer, was at home on 25 May, 2020, when he was called to the intersection outside Cup Foods, where Mr Floyd was suspected of passing a fake $20 bill earlier in the evening.
He arrived just before 10pm, about half an hour after Mr Floyd had been declared dead at a downtown hospital. He said he helped ensure that evidence at the scene was properly secured and any witnesses were found.
Mr Zimmerman said officers were responsible for the care of anyone they arrested and are trained to give first aid to an injured or distressed detainee even if they know an ambulance is coming.
"His safety is your responsibility, his wellbeing is your responsibility," he told the jury.
He described how officers are trained only to respond to any threat with a proportionate amount of force.
"Once a person is cuffed, the threat level goes down all the way," Mr Zimmerman testified. "They're cuffed. How can they really hurt you, you know?"
He warned of the dangers of leaving a person in a prone position.
Posters are zip-tied to the security fence around the heavily secured Hennepin County Courthouse during the trial of Derek Chauvin. Source: Getty Images
"Once you've secured or handcuffed a person you need to get them out of the prone position as soon as possible because it restricts their breathing," he said.
He offered harsh testimony against the way his former colleague and other officers at the scene restrained Mr Floyd.
"Pulling him down to the ground face down, and putting your knee on the neck for that amount of time is just uncalled for," Mr Zimmerman said. "I saw no reason why the officers felt they were in danger, if that's what they felt, and that's what they would have to feel in order to use that kind of force."
In cross-examination, Mr Zimmerman agreed when Eric Nelson, Mr Chauvin's lead lawyer, said the lieutenant does not train officers in how to use restraints and that as an investigator he has to use force less often than a patrolling officer.
Mr Nelson has argued that angry bystanders shouting at Mr Chauvin to check Mr Floyd's pulse could have distracted him and other officers from the care of Mr Floyd.
Mr Zimmerman said, "It doesn’t matter about the crowd as long they’re not attacking you. The crowd really shouldn’t have an effect on your actions."
The court adjourned early with testimony due to resume on Monday.
